The health care field is experiencing a heightened awareness of problems presented by mercury, nitrous oxide, AIDS, herpes, and many other undesirable contaminants which are found in the work rooms of health care professionals. Sterilization of work tools and work surfaces has heretofore been accomplished by the use of liquid antibacterial soaking and cleaning compounds, as well as various air filtering systems. The air filtering systems were partially effective in removing large molecular weight bacterial antigens, however, they have been unable to remove elemental mercury, nitrous oxide, and ozone, which further have deleterious effects.
The Occupational Safety Health Act of 1970 (OSHA), discloses contamination levels for mercury in the dental profession, and defines "contaminated" as levels that exceed the Threshold Limit Value (TLV) of 0.05 milligrams per cubic meter. Although the effects of mercury poisoning in industrial settings has been documented, the incidents and effects of mercury poisoning in dental offices has only recently been studied. Chronic inhalation of mercury vapor effects primarily the central nervous system, although the kidneys, which accumulates the absorbed mercury, are also effected The symptoms of mercury poisoning from chronic inhalation develop gradually, and thus may be difficult to notice. With the exception of tremors, the symptoms may be ignored by the victim or attributed to other causes This lack of awareness is particularly likely in the case of erethism, a condition characterized by irritability, outbursts of temper, excitability, shyness, resentment of criticism, headache, fatigue, and indecision.
Micromercurialism is said to account for psychological changes observed in persons frequently exposed to low concentrations of mercury in the air, such as concentrations found in the majority of dental offices. Micromercurialism is characterized by decreased productivity, loss of memory, loss of self-confidence, depression, fatigue and irritability.
Mercury vapors in the dental office may pose a serious threat to pregnant dentists, dental assistants, hygienists and receptionists. The primary source of mercury vapor in a dental office is from the practice of hand mulling and squeezing excess mercury from the amalgamation process. In more modern dental offices, high speed amalgamation, using a 1:1 mercury-alloy ratio still results in mercury contamination from spillage, vapors which escape from improper storage, and most notably, the high concentration of mercury vapor in aerosols produced during the removal of old restorations. The high speed drills which are used in this process not only remove the old filling, but also disburse mercury vapor and minute particles into the working environment, and especially spray the contaminated aerosol directly into the face of the dentist, his or her assistant and the hygienist.
In solving the problems related to the used of mercury, recommendations have been made that the dentist provide for a yearly examination for mercury present in the bodies of anyone in the contaminated work space. A further recommendation is for the dentist to have periodic mercury surveys of the work spaces.
Indirect contamination occurs in contemporary dental offices and more modern buildings because there is an increased potential for sustaining unexceptably high concentrations of mercury. Modern dental offices are complete with rugs, return air ventilation systems, amalgamator cabinets, and nearly air-tight ventilation systems in an attempt to be energy conscious.
Rugs or carpeting promote continuing contamination when mercury from a spillage settles into a carpet, because total decontamination is extremely difficult, if not impossible. Vacuuming and walking on the rugs heighten the contamination problem. Vacuum cleaners merely agitate the substances to form mercury vapor, which pass directly through the bag and exhaust and are disbursed throughout different areas of the office.
It has been reported in the ADA Journal that 1 out of 7 dental offices is contaminated to the extent that dental personnel are exposed to hygienally significant amounts of mercury vapor throughout the day. Gronka, et al., Mercury Vapor Exposure in Dental Offices, JADA 81;923, Oct. 1970.
Office ventilation systems include return air conduits for heating and cooling which merely recirculate the air. Recirculation helps to lower heating bills, and is included in many modern office buildings. Because dentists tend to have offices in more modern buildings, this problem compounds itself when mercury contamination from a dental office is spread throughout the air ventilation systems in a building to contaminate other offices which share the same building. Contaminated mercury is therefore distributed among the other offices, as well as the dental office itself. These ventilation systems generally include filters for the removal of dust, pollen, and other particulate matters, but do not contain any filtering means for removing elemental mercury or other low weight contaminants. A particle of dust is hundreds of thousands of times larger than the particles of mercury vapor, and are therefore much easier to trap for collection and disposal.
For reasons discussed above, it would be very advantageous to have a means for removing mercury vapor and other toxins, such as nitrous oxide and ozone, as well as pollen, dust and airborne pathogenic bacteria. In the past, filters to be placed in a contaminated room have been commercially available. However, these filters have been very expensive, and require the filter be changed every thirty days. The filter design of the previous systems become easily saturated because very little active area is allowed to come in contact with the contaminated air for removal of the mercury vapor.
In addition, health care professionals are becoming increasingly concerned with the transmission of AIDS, herpes and the air route spreading of pathogenic bacteria in their working environment. Patients are similarly concerned with bacteria left behind by previous patients. It would be advantageous to disinfect and inactivate these viruses, bacteria and infectious diseases by exposing and filtering the air before it reenters the work station or laboratory. Control of the air route of spread of pathogenic bacteria in the operating room was described by Deryl Hart, M.D. and reported in Review of Surgery, November-December, 1966, pages 381-392, in which it is stated that bactericidal ultraviolet radiation destroys or attenuates the pathogens which continually enter the air in the environs of human beings. The ultraviolet radiation was found to be effective against many pathogenic fungi and bacteria. Within dental laboratory environs, operations take place which expel bodily fluids containing such bacteria into the atmosphere. Frequent air changes and filtering may be performed in an attempt to reduce the concentration of the contaminants produced during such operations.
U.S. Pat. No. 3,194,629, issued July 13, 1965 to Dreibelbis et al., discloses a process of removing mercury from a gas by passing the gas over activated carbon impregnated with sulfur.
U.S. Pat. No. 3,568,416, issued Mar. 9, 1971 to Staunton, discloses a filter assembly including a honey-comb structure having a plurality of passages therein aligned in the direction of air flow. Some of the passages in the honey-comb structure are filled with granular filter material, such as activated carbon, while the other passages remain unfilled.
U.S. Pat. No. 3,630,007, issued Dec. 28, 1971 to Newmann, discloses a disposable active charcoal filter having a frame open at both sides and subdivided into a plurality of compartments by intersecting partitions. The two open sides are covered by gas permeable sheets, and the space between the sheets is filled with active carbon.
U.S. Pat. No. 3,956,458, issued May 11, 1976 to Anderson, discloses an apparatus for the collection and removal of mercury vapor from the air. Atmospheric air conditioning mercury vapor is forced by a blower through a sulfur filter, through an electrostatic precipitator, and into an iodine impregnated, activated charcoal filter.
U.S. Pat. No. 4,139,354, issued Feb. 13, 1979 to Giles, discloses a small annular-shaped filter specially designed for use in controlled atmosphere working enclosures of the type used in dental operatories and the like for performing mercury handling operations. The filter is removably mounted within the air outlet parts of the work enclosures and contains a filtering material specially developed for mercury vapor from the air passing through the filter.
U.S. Pat. No. 4,419,107, issued Dec. 6, 1983 to Roydhouse, discloses a mercury filter for collecting low concentration mercury vapor and gas. The filter has an absorber having a collecting surface of a material that amalgamates readily with mercury, the surface having a reactive tarnish produced by exposure of the plates to available iodine. The absorber may have spaced collecting members with the gas passing about the collecting members. Optionally, at least one of the collecting members is at a higher electrical potential difference than the remaining member, which potential difference is insufficient for the filter to act as an electrostatic precipitator so as to reduce attraction of dust.
Great Britain Pat. No. 1,225,751, issued to Marshall, discloses a filter for filtering gaseous streams, such as air, to remove radioactive particles or chemical substances from a fluid stream. The filter comprises two or more plies of honey-comb material which is slightly offset relative to one another. The cells in the honeycomb structure plies contain granules of activated carbon.
The objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings.